Downhole Apparatus

ABSTRACT

A downhole cementing apparatus ( 10 ) comprises a body ( 18 ) and a sealing arrangement ( 20 ) mounted on the body. The cementing apparatus ( 10 ) is deployable through a downhole tool ( 12 ) with a volume of cement ( 14 ). The sealing arrangement ( 20 ) is configured to define a varying point of sealing contact axially along the sealing arrangement with an inner surface of a downhole tool ( 12 ) as the cementing apparatus ( 10 ) is deployed through said tool.

FIELD OF INVENTION

The present invention relates to the transport of a fluid, such ascement, through a downhole tool or assembly.

BACKGROUND TO INVENTION

In the oil and gas exploration and production industry, well boreholesare drilled from surface in order to access subsurfacehydrocarbon-bearing formations. A tubular string, such as a completionstring, may be run into the borehole and the annulus between the outsideof the string filled with a fluid, such as cement. Cementing operationsmay be required at various instances during the life cycle of a well,for example to assist in securing and supporting the string in theborehole during its initial completion, to prevent uncontrolledmigration of fluid in the annulus, to provide isolation of one or moreformation zone during production, and/or during remedial or workoveroperations.

Completion strings beneficially provide the ability to perform a numberof different operations in the borehole, the various completion stringtools utilising a variety of activation mechanisms and systems.

However, since many completion string tools extend into or requireaccess to an axial throughbore or flow passage of the string, thesetools and associated equipment represent an obstruction to the passageof cement. As such, the ability to direct cement to the desired locationmay be impaired or prevented.

Moreover, there is a significant drive to improve the effectiveness andreliability of tools which are deployed and operated in a downholeenvironment, for example to ensure that the tools operate at maximumefficiency, have minimum risk of failure or imprecise operation, can beflexible according to operator requirements, and minimise any necessaryremedial action, associated time delays and costs. Thus, it is importantalso that substantially all of the cement is directed through thestring, such that the subsequent efficient operation of the tools anddownhole equipment is not impaired.

SUMMARY OF INVENTION

Aspects of the present invention relate to apparatus and methods for usein transporting a fluid, such as cement, through a downhole tool orassembly. In particular, but not exclusively, embodiments of theinvention relate to methods and apparatus for transporting cementthrough a downhole tool used in the treatment, for example fracturing,of a subterranean formation.

According to a first aspect of the present invention there is provided adownhole cementing apparatus deployable through a downhole tool with avolume of cement, comprising:

a body; and

a sealing arrangement mounted on the body and configured to define avarying point of sealing contact axially along the sealing arrangementwith an inner surface of a downhole tool as the cementing apparatus isdeployed through said tool.

Providing a varying point of sealing contact axially along the sealingarrangement may permit a seal to be provided at all times during passageof the apparatus through the downhole tool.

The sealing arrangement may comprise a unitary seal member or structure,wherein said seal member or structure defines a plurality of sealregions of features configured to establish sealing contact with aninner surface of a downhole tool.

The sealing arrangement may comprise at least one seal member forsealingly engaging the inner surface of the downhole tool. At least oneseal member may be operable to swab or wipe the inside of the downholetool during deployment through said tool. The seal members may be spacedso that at least one seal member may provide sealing contact with theinner surface of the downhole tool during deployment through said tool.

The sealing arrangement may comprise a plurality of seal membersarranged along the body. The seal members may be spaced so that the sealmember employed to provide the sealing contact varies as the apparatusis deployed through the downhole tool. For example, the seal members maybe spaced so that where one seal member is adjacent to the portion ofthe downhole tool which may otherwise result in fluid bypass, at leastone other of the seal members is positioned adjacent to a portion of thedownhole tool which permits a sealing contact to be provided between theapparatus and the downhole tool, thus ensuring that a sealing contact isprovided at all times during passage of the apparatus through thedownhole tool. When used in a cementing operation, for example, ensuringthat a sealing contact is provided/maintained may ensure that the cementis efficiently driven through the downhole tool and so eliminate or atleast mitigate the possibility that cement will set in the tool and soimpair the cementing operation and/or subsequent operation of downholetools and equipment.

The sealing contact may be formed by a continuous circumferential sealbetween the seal member and the downhole tool. In use, the apparatus maybe configured so that the sealing contact isolates a downstream portionof the downhole tool from an upstream portion of the downhole tool.

The apparatus may isolate fluid located downstream of the sealingcontact from the upstream portion of the downhole tool.

In particular embodiments, the downstream fluid may comprise cement tobe urged through the downhole tool. Additionally or alternatively, thedownstream fluid may comprise a driving fluid, such as glycol, water,drilling mud or other suitable driving fluid. Additionally oralternatively, the downstream fluid may comprise an inhibitor such assugar grease or the like. Beneficially, providing sugar grease mayprevent or inhibit adherence of cement to the downhole tool or otherdownhole equipment. Thus, an apparatus according to the presentinvention may be disposed behind a column of fluid and operable to drivethe fluid through the downhole tool.

Any suitable means for deploying the apparatus through the downhole toolmay be used. For example, the apparatus may be deployed or urged throughthe downhole tool by a fluid. In particular embodiments, the apparatusmay be deployed or urged through the downhole tool by a fluid pressure,for example a fluid pressure acting across the sealing contact. Theapparatus may be configured for deployment through the downhole tool byan upstream fluid. The upstream fluid may comprise a driving fluid, suchas glycol, water, drilling mud or other suitable driving fluid.Additionally or alternatively, the upstream fluid may comprise aninhibitor such as sugar grease or the like. Alternatively oradditionally, the upstream fluid may comprise cement or the like. Thus,in some instances an apparatus according to the present invention may bedisposed ahead of a column of fluid, the apparatus being deployed bysaid fluid.

The apparatus may alternatively or additionally comprise or be coupledto mechanical means for deploying the apparatus through the downholetool. For example, the apparatus may be coupled to a work string or thelike for urging the apparatus through the downhole tool.

The apparatus, and more particularly at least one of the seal members,may be configured to swab or wipe the inside of the downhole tool. Forexample, the apparatus may be configured to remove any cement depositsfrom the downhole tool as the apparatus is deployed therethrough.

The seal members may be of any suitable form or construction.

The radial extent of the seal members may be configured such that at afirst axial location in the downhole tool one of the seal memberscooperates with the downhole tool to provide a sealing contact and at asecond axial location within the downhole tool said seal member permitspassage of fluid and at least one other of the seal members cooperateswith the downhole tool to provide a sealing contact.

The radial extent of the seal member may be configured such that at afirst axial location in the downhole tool a first seal member cooperateswith the downhole tool to provide a sealing contact, and at a secondaxial location within the downhole tool the first seal member may notprovide sealing contact and a second seal member cooperates with thedownhole tool to provide a sealing contact.

In some embodiments, two or more of the seal members may extend radiallyto the same diameter. In particular embodiments, one or more of the sealmembers may extend to a different radial extent than at least one otherof the seal members. The radial extent of each seal member may beselected according to the downhole tool.

In particular embodiments, one or more of the seal members may beconfigured to define a cup shape. One or more of the seal members may beconfigured to define a disc shape.

In particular embodiments, the apparatus may comprise five seal members,although it will be recognised that the apparatus may alternativelycomprise two seal members, three seal members, four seal members or morethan five seal members.

The seal members may be disposed on a mandrel. Any suitable means fordisposing the seal members on the mandrel may be provided. One or moreof the seal members may be integrally formed with the mandrel. One ormore of the seal members may be secured to the mandrel. One or more ofthe seal members may be configured to slip over the mandrel. One or moreof the seal member may be moulded onto the mandrel. One or more of theseal members may engage the mandrel by an interference fit, may beshrink fitted onto the mandrel.

The mandrel may comprise a unitary component. The mandrel may compriseat least one module.

Alternatively, and in particular embodiments, the mandrel may comprise aplurality of modules. In particular embodiments, a module may beassociated with each of the seal members. For example, each of the sealmembers may be mounted or otherwise provided on its own module.Alternatively, a module may be associated with a plurality of the sealmembers. At least one module may support at least one seal member. Inembodiments where the apparatus comprises seal members of different typeor form, for example but not exclusively of different shape or radialextent, a module may be associated with each seal member type. Themodules and/or the seal members of each type may comprise an identifier.Providing an identifier may facilitate ready identification of eachmodule and/or seal members or of at least one module or seal member, forassembly or inventory purposes for example.

The apparatus may comprise one or more spacer configured to provide theaxial spacing between the seal members. The spacer may comprise a moduleof the mandrel.

A connection arrangement may be provided for coupling the mandrel toadjacent components and/or for coupling modules of the mandrel together.The connection arrangement may be provided for coupling at least twomodules of the mandrel together. The mandrel may comprise at least onespacer for providing an axial spacing between at least two seal members.

The connection arrangement may comprise a female connector.

The connection arrangement may comprise a male connector. In particularembodiments, each module may comprise a male connector and a femaleconnector.

The connection arrangement may comprise a threaded connection, push fitconnector or the like.

The downhole tool may be of any suitable form or construction.

The downhole tool may for example comprise a tool for use in treating asubterranean formation. The downhole tool may comprise a tool for use ishydraulic fracturing. Hydraulic fracturing, commonly known as“fracking”, may involve the injection of fluid into the formation topropagate fractures in the formation rock and increase flow ofhydrocarbons into the borehole for extraction. In use, one or morefracturing tools may be run into the borehole and located adjacent tothe formation. Fluid may then be directed through ports in a sidewall ofthe fracturing tool and injected into the formation. In some instances,a number of fracturing tools may be located at different axially spacedpositions in a tubular string and configured to facilitate fracturing ofmultiple and/or selected formations.

The downhole tool may comprise a tool housing defining a central boreand including a fluid port. The fluid port may be configured to permitfluid communication between the central bore and a location external tothe housing. The fluid port may extend in any suitable direction. Thefluid port may extend generally perpendicularly relative to the centralbore. In some embodiments the fluid port may extend generally obliquelyrelative to the central bore. The fluid port may extend in varyingdirections, for example portions of the fluid port may extend at leastone of perpendicularly, parallel and obliquely relative to the centralbore.

A valve member, such as a valve sleeve may be mounted within thehousing. The valve member may be moveable, for example axially moveable,from a closed position in which the fluid port is blocked to an openposition in which the fluid port is opened. The fluid port may be openedto provide fluid communication between the central bore of the tool andan external downhole location, such as an annulus, a surroundingformation or the like. The fluid port may be arranged to accommodate oneor both of outflow and inflow.

The downhole tool may comprise a catching apparatus, such as provided inaccordance with any other aspect. The catching apparatus may be mountedwithin the housing, for example on a downhole side of the valve member.

The downhole tool may comprise an indexing mechanism mounted within thehousing. The indexing mechanism may be located on an uphole side of thevalve member. The indexing mechanism may be arranged to be moved axiallyalong the housing towards an actuation site. Upon reaching the actuationsite the indexing mechanism may initiate actuation, for examplemovement, of at least one of the valve member and the catchingapparatus.

The downhole tool may define a downhole fracturing tool.

The downhole tool may comprise a tool as disclosed in WO 2011/117601and/or WO 2011/117602, which are incorporated herein by reference.

In use, the apparatus may be configured for deployment through an axialflow passage or throughbore of the downhole tool.

The axial flow passage of the downhole tool may comprise or define avarying profile. The axial flow passage may comprise a first portion ofa first diameter and a second portion of a second, larger, diameter. Thesecond portion may comprise a recess. In particular embodiments, theprofile may comprise an indexing profile.

Providing an apparatus according to embodiments of the present inventionmay permit a sealing contact to be provided and maintained in an axialflow passage having such a varying profile, since the seal members maybe spaced so that where one seal member is adjacent to the profileportion which may otherwise result in fluid bypass, at least one otherof the seal members is positioned adjacent to a portion of the downholetool which permits a sealing contact to be provided between theapparatus and the downhole tool, thus ensuring that a sealing contact isprovided at all times during passage of the apparatus through thedownhole tool.

Alternatively or additionally, a restriction may be provided in thedownhole tool and the apparatus may be configured for deployment throughthe restriction. The restriction may comprise part of the downhole tooldisposed in or extendable into the axial flow passage. Alternatively, oradditionally, the restriction may comprise a tool disposed within theaxial flow passage. The restriction may define a flow passage other thanthe axial flow passage which may, for example, define a leak path. Inparticular embodiments, the restriction may comprise a sleeve, such as acollet sleeve.

Providing an apparatus according to embodiments of the present inventionmay permit a sealing contact to be provided and maintained in an axialflow passage having such a restriction, since the seal members may bespaced so that where one seal member is adjacent to the profile portionwhich may otherwise result in fluid bypass, at least one other of theseal members is positioned adjacent to a portion of the downhole toolwhich permits a sealing contact to be provided between the apparatus andthe downhole tool, thus ensuring that a sealing contact is provided atall times during passage of the apparatus through the downhole tool.

An inhibitor may be provided to prevent or mitigate adherence/setting ofthe fluid, such as cement, to the apparatus and/or the downhole tool.The inhibitor may comprise sugar grease or the like. Sugar grease hasbeen found to be particularly effective in preventing adherence ofcement to downhole tools and equipment. The inhibitor may be disposed onthe downhole tool. The inhibitor may be disposed on the apparatus. Theinhibitor may be provided in the form of a coating.

The downhole tool may be coupled to or form part of a tubular string,such as a completion string.

A single downhole tool may be provided. In particular embodiments, aplurality of downhole tools may be provided. In embodiments where thedownhole tool comprises a tool for treating, for example fracturing, asubterranean formation may comprise up to 30 downhole tools, for exampleup to 150 downhole tools.

A single apparatus may be provided. In particular embodiments, aplurality of downhole tools may be provided. In embodiments where aplurality of the downhole tools are provided, one apparatus may beprovided for each downhole tool.

According to a second aspect of the present invention there is provideda method comprising:

providing a body;

mounting a sealing arrangement on the body;

configuring the sealing arrangement such that where the cementingapparatus is deployed through a downhole tool the sealing arrangementdefines a varying point of sealing contact axially along the sealingarrangement with an inner surface of a downhole tool.

The sealing arrangement may comprise a plurality of axially spaced sealmembers. At a first axial location within the downhole tool, one of theseal members is located to cooperate with the downhole tool to provide asealing contact. At a second axial location within the downhole toolsaid seal member permits passage of fluid and at least one other of theseal members cooperates with the downhole tool to provide a sealingcontact.

The method may comprise urging a fluid, such as cement or the like,through the downhole tool. The method may comprise or form part of acementing operation in a borehole, such as a well borehole.

The method may comprise treating, for example fracturing, a subterraneanformation.

According to third aspect of the present invention there is provided adownhole method comprising:

-   -   deploying an apparatus through a downhole tool, wherein the        apparatus comprises a sealing arrangement;

establishing a point of sealing contact between the sealing arrangementand an inner surface of the downhole tool; and

varying the point of sealing contact axially along the sealingarrangement during deployment through the downhole tool.

The method may comprise providing the varying point of sealing contactbetween a plurality of axially spaced seal members within the sealingarrangement.

At a first axial location within the downhole tool, a first seal membermay cooperate with the downhole tool to provide a first point of sealingcontact. At a second axial location within the downhole tool the firstpoint of sealing contact may be removed, and a second seal member maycooperate with the downhole tool to provide a second point of sealingcontact.

The method may comprise pumping the apparatus through the downhole tool.

The method may comprise passing a volume of cement through the downholetool on one axial side of the apparatus.

The method may comprise:

deploying first and second apparatuses through the downhole tool,wherein each apparatus may include a respective sealing arrangement;

deploying a volume of cement intermediate the first and secondapparatuses;

establishing a point of sealing contact between the respective sealingarrangements and an inner surface of the downhole tool; and

varying the respective points of sealing contact axially along therespective sealing arrangements during deployment through the downholetool.

The method may comprise or form part of a downhole cementing operation.

The method may comprise treating a subterranean formation via thedownhole tool.

The downhole tool may comprise a tool for use in fracturing asubterranean formation.

According to a fourth aspect of the present invention there is provided:

a downhole tool; and

an apparatus for deployment through the downhole tool, the apparatuscomprising a plurality of axially spaced seal members, wherein the axialspacing of the seal members is configured such that at a first axiallocation in the downhole tool one of the seal members cooperates withthe downhole tool to provide a sealing contact and at a second axiallocation within the downhole tool said seal member permits passage offluid and at least one other of the seal members cooperates with thedownhole tool to provide a sealing contact.

According to a fifth aspect of the present invention there is providedan apparatus for deployment through a downhole tool, the apparatuscomprising a plurality of axially spaced seal members, wherein the axialspacing of the seal members is configured such that at a first axiallocation in the downhole tool one of the seal members cooperates withthe downhole tool to provide a sealing contact and at a second axiallocation within the downhole tool said seal member permits passage offluid and at least one other of the seal members cooperates with thedownhole tool to provide a sealing contact.

According to a sixth aspect of the present invention there is provided adownhole system, comprising:

a downhole tool; and

an apparatus for deployment through the downhole tool, wherein theapparatus comprises a sealing arrangement configured to define a varyingpoint of sealing contact axially along the sealing arrangement with aninner surface of the downhole tool during deployment through said tool.

The apparatus may comprise a plurality of axially spaced seal members,wherein the axial spacing of the seal members may be configured suchthat at a first axial location in the downhole tool one of the sealmembers cooperates with the downhole tool to provide a sealing contactand at a second axial location within the downhole tool said seal memberpermits passage of fluid and at least one other of the seal memberscooperates with the downhole tool to provide a sealing contact.

The downhole tool may comprise a tool for use in treating a subterraneanformation, a tool for use in hydraulic fracturing, a tool housingdefining a central bore and including a fluid port, a valve sleeve, acatching apparatus and/or an indexing mechanism, or the like.

According to a seventh aspect of the present invention there is provideda method comprising deploying an apparatus having a plurality of axiallyspaced seal members through a downhole tool, wherein at a first axiallocation within the downhole tool one of the seal members is located tocooperate with the downhole tool to provide a sealing contact and at asecond axial location within the downhole tool said seal member permitspassage of fluid and at least one other of the seal members cooperateswith the downhole tool to provide a sealing contact.

An eighth aspect of the present invention relates to use of an inhibitorto prevent adherence of cement to downhole equipment.

The downhole equipment may comprise an apparatus according to anyprevious aspect.

The downhole equipment may comprise a downhole tool according to anyprevious aspect.

The inhibitor may comprise sugar grease.

According to a ninth aspect of the present invention there is provided amethod for inhibiting adherence of cement to a downhole tool of astring, comprising coating a surface of the tool with sugar grease.

The method may comprise directing a volume of sugar grease through thestring. The downhole tool may comprise a tool for use in treating asubterranean formation, a tool for use in hydraulic fracturing, a toolhousing defining a central bore and including a fluid port, a valvesleeve, a catching apparatus, and/or an indexing mechanism, or the like.

The method may comprise directing a volume of cement through thedownhole tool. The method may comprise using a downhole apparatuscomprising a body and a sealing arrangement mounted on the body todirect sugar grease through the downhole tool.

According to a tenth aspect of the present invention there is provided adownhole cementing method, comprising:

directing a volume of cement through a string comprising a fracturingtool; and

directing the cement into an annulus surrounding at least a portion ofthe string.

The method may comprise performing a fracturing operation after thecement has been directed into the annulus.

The method may comprise deploying an apparatus according to any otheraspect through the string with the volume of cement.

The method may comprise disposing a first apparatus on a downhole sideof the volume of cement.

The method may comprise disposing a second apparatus on an uphole sideof the cement.

The method may comprise coating surfaces of the fracturing tool with aninhibitor configured to inhibit adherence of cement to the surface.

The inhibitor may comprise sugar grease.

An eleventh aspect of the present invention relates to a downholeapparatus deployable through a downhole tool. The apparatus may bedeployable with a volume of a fluid. The apparatus may comprise a body.The apparatus may comprise a sealing arrangement mounted on the body.The sealing arrangement may be configured to define a sealing contactwith an inner surface of a downhole tool. The sealing arrangement may beconfigured to provide a varying point of sealing contact along a lengthof the sealing arrangement as the apparatus is deployed through saidtool.

It should be understood that the features defined above in accordancewith any aspect of the present invention or below in relation to anyspecific embodiment of the invention may be utilised, either alone or incombination with any other defined feature, in any other aspect orembodiment of the invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 a longitudinal sectional view of a downhole cementing apparatusaccording to an embodiment of the present invention;

FIG. 2 a longitudinal sectional view of the downhole cementing apparatusshown in FIG. 1, shown disposed within a downhole tool;

FIG. 3 an enlarged view of a first, uphole, end region of the downholetool, showing the cementing apparatus at a first axial location;

FIG. 4 an enlarged view of a second, downhole, end region of thedownhole tool;

FIG. 5 a cross sectional view of the apparatus and downhole tool alongsection A-A shown in FIG. 4;

FIG. 6 a diagrammatic view of a wellbore system, in which embodiments ofthe present invention may be utilised;

FIG. 7 a diagrammatic view of the wellbore system of FIG. 6, shownduring a cementing operation;

FIG. 8 a diagrammatic view of the wellbore system of FIGS. 7 and 8,shown after a cementing operation has been completed;

FIG. 9 a diagrammatic view of the wellbore system of FIGS. 7, 8 and 9,shown during a fracturing operation.

DETAILED DESCRIPTION OF DRAWINGS

Referring first to FIGS. 1 and 2, there is shown a downhole cementingapparatus, in the form of a cement dart 10, according to an embodimentof the present invention. In use, the dart 10 may be employed during adownhole cementing operation, the dart 10 being deployable through adownhole tool 12 (FIG. 2) with a volume of cement 14 and configured toprovide a varying point of sealing contact 16 between the dart 10 andthe downhole tool 12 which permits the cement 14 to be driven throughthe downhole tool 12.

As shown in FIG. 1, the dart 10 comprises a body in the form of amandrel 18 and a sealing arrangement 20 for providing the sealingcontact 16. In the illustrated embodiment, the sealing arrangement 20comprises a plurality of axially spaced seal members 22 a, 22 b, 22 c,22 d, 22 e and, in use, the dart 10 is configured so that as the dart 10is deployed though the downhole tool 12 the point of sealing contact 16between the dart 10 and the tool 12 varies axially along the sealingarrangement 20, thus ensuring that a sealing contact between the dart 10and the tool 12 is maintained at all times during passage of the dart 10through the tool 12.

The mandrel 18 comprises a number of separate modules 24 a, 24 b, 24 c,24 d, 24 e, 24 f and 24 g. In the illustrated embodiment, the modules 24a, 24 b, 24 c, 24 d and 24 e comprise seal member modules, each having aseal member 22 a, 22 b, 22 c, 22 d, 22 e disposed or formed thereonwhile the modules 24 f and 24 g comprise spacer modules. Each of themodules 24 a to 24 g has a male connector 26 a, 26 b, 26 c, 26 d, 26 e,26 f and a corresponding female connector 28 a, 28 b, 28 c, 28 d, 28 e,28 f and 28 g for coupling the modules 24 a, 24 b, 24 c, 24 d, 24 e, 24f and 24 g together and which permits the dart 10 to be constructed withthe spacing required to provide the required sealing contact 16.

The axial spacing of the seal members 22 a, 22 b, 22 c, 22 d, 22 e isconfigured so that the point of sealing contact 16 between the dart 10and the axial flow passage 14 of the tool 12 is maintained by at leastone of the seal members 22 a, 22 b, 22 c, 22 d, 22 e at all times duringpassage of the dart 10 through the downhole tool 12. Providing andmaintaining the seal 16 ensures that the cement 14 is driven through thedownhole tool 12, even where one or more of the seal members 22 a, 22 b,22 c, 22 d, 22 e is disposed at an axial location in the downhole tool12 which may permit fluid passage around the respective seal member 22a, 22 b, 22 c, 22 d, 22 e.

In the illustrated embodiment, each seal member 22 a to 22 e comprises acup-shaped seal element 30 a, 30 b, 30 c, 30 d, 30 e moulded orotherwise disposed on its respective mandrel portion 24 a to 24 e. Theseal elements 30 a to 30 e each define a cup angle θa, θb, θc, θd, θewith respect to the mandrel 18 and define a maximum diameter Da, Db, Dc,Dd, De at their distal ends 32 a, 32 b, 32 c, 32 d, 32 e. The cup anglesθa, θb, θc, θd, θe and the diameters Da, Db, Dc, Dd, De may beconfigured so that the point of sealing contact 16 between the dart 10and the axial flow passage 14 of the tool 12 is maintained by at leastone of the seal members 22 a, 22 b, 22 c, 22 d, 22 e at all times duringpassage of the dart 10 through the downhole tool 12.

Referring now in particular to FIGS. 2 to 4, the downhole tool 12comprises a housing 34 which defines a central bore 36 and extendsbetween an uphole connector 38 and a downhole connector 40. Theconnectors 38, 40 facilitate connection of the tool 12 to an upholestring component S1 and a downhole string component S2 (shownschematically in FIG. 1).

Fluid ports 42 are provided radially through a wall of the housing 34and, when opened, the ports 42 facilitate outflow of a fluid from thecentral bore 36 of the housing 34. A valve member in the form of asleeve 44 is moveable axially along the housing 34 from a closedposition in which the sleeve 44 blocks or closes the ports 42, to anopen position. Movement of the sleeve 44 towards its open position isachieved by an associated actuator portion 46.

A catching sleeve 48 is located downhole of the valve sleeve 44 and ismoveable from a free configuration in which an object, such as a ball(not shown) may freely pass, to a catching configuration in which anobject, such as a ball, may be caught. In use, the catching sleeve 48may function to catch an object and establish diversion of any fluidfrom the central bore 36 outwardly through the fluid ports 42 when open.Further, the catching sleeve 48 is operated to move to its catchingconfiguration by movement of the valve sleeve 44 towards its openconfiguration.

The actuator portion 46 of the tool 12 defines an indexing profile 50provided on the inner surface of the housing 34.

The indexing profile 50 includes a plurality of axially spaced annularrecesses 52 a, 52 b, 52 c, 52 d, 52 e, 52 f, 52 g, 52 h formed in theinner surface of the housing 34. An indexing sleeve 54 is mounted withinthe housing 34 and is configured to cooperate with the indexing profile50 to be driven in a number of discrete linear movement steps throughthe housing 34 by passage of a corresponding number of actuationobjects, such as balls. The indexing sleeve 54 is driven in discretemovement steps until reaching an actuation site within the tool 12,where the indexing sleeve 54 engages and moves the valve sleeve 44 in adownhole direction to open the ports 42.

In the illustrated embodiment, the indexing sleeve 50 includes a tubularwall structure 56 which defines a central bore 58 corresponding with thecentral bore 36 of the housing 34. The central bore 58 is sized topermit an actuation object, such as a ball, to pass therethrough.

The indexing sleeve 54 also includes first and second circumferentialarrays of engagement members 60, 62 which are arranged such that thearray of first engagement members 60 are axially spaced apart from thearray of second engagement members 62. The engagement members arearranged within slots 64, 66 formed through the wall structure 56. Inuse, the arrays of engagement members 60, 62 cooperate with the indexingprofile 50 of the housing 34 to be sequentially engaged by a passingobject, such as a ball, to drive the indexing sleeve 54 one discretelinear movement step. More specifically, the first and second arrays ofengagement members 60, 62 are arranged to be moved radially within theirassociated slots 64, 66 such that each array of engagement members 60,62 is moved in an alternating or out of phase manner relative to theother array of engagement members 60, 62 by cooperation with theindexing profile 50 during movement of the indexing sleeve 54 throughthe housing 34. Such alternating radial movement alternately moves thefirst and second arrays of engagement members 60, 62 radially inwardlyand into the central bore of the indexing sleeve 54, to thus besequentially engaged by a passing actuation object. In this way, apassing object may engage the engagement members 62,64 of one of thefirst and second arrays to move the indexing sleeve 54 a portion of adiscrete movement step, and then subsequently engage the engagementmembers 62, 64 of the other one of the first and second arrays tocomplete the discrete movement step of the indexing sleeve 54.

The engagement members 62, 64 are mounted on the distal end ofrespective collet fingers 68 which are secured at their proximal ends tothe tubular wall structure 56. The collet fingers 68 are resilientlydeformable to facilitate radial movement of the engagement members 62,64 by cooperation with the indexing profile 50.

In the illustrated embodiment the collet fingers 68 are unstressed whenthe engagement members 62, 64 are positioned radially outwardly and thusremoved from the central bore. As such, the collet fingers 68 must bepositively deformed by appropriate cooperation between the engagementmembers 62, 64 and the indexing profile 50 to move the engagementmembers 62, 64 radially inwardly into the central bore to permitengagement by an actuation object, such as a ball. In such anarrangement, the collet fingers 66 may function to bias the engagementmembers 62, 64 in a direction to be moved radially outwardly from thecentral bore. Each slot of the indexing sleeve 54 accommodates tworespective engagement members 62, 64. Further, the slots are definedbetween respective elongate ribs. Each rib includes a spline feature orkey which are received in corresponding longitudinally extending slotsor key-ways (not shown) formed in the housing 34. Engagement between thekeys and the longitudinal slots or key-ways may function to rotationallylock the indexing sleeve 54 relative to the housing 34, while stillpermitting movement of the indexing sleeve 54 linearly through thehousing 34. Such an arrangement may facilitate milling of the indexingsleeve 54, if ever required.

It will be recognised that the downhole tool 12 may thus include aprofile, such as the indexing profile 50, or a restriction through whicha dart must pass, such as the catching sleeve 48 or indexing sleeve 50,but which may prevent the creation of a continuous circumferential seal.In the case of a restriction, for example, fluid leakage may bepermitted around the restriction and so prevent the creation of acontinuous circumferential seal. Alternatively or additionally, the formof the restriction, which may for example comprise a collet sleeve orthe sleeve, may prevent the creation of a continuous circumferentialseal.

In embodiments of the present invention, however, the dart 10 isconfigured to provide a varying point of sealing contact 16 axiallyalong the sealing arrangement 20 which permits a sealing contact 16 tobe provided at all times during passage of the dart 10 through thedownhole tool 12.

Deployment of the dart 10 through the downhole tool 12 will now bedescribed.

In FIG. 3, the dart 10 is shown located within the axial flow passage 14of the downhole tool 12 at a first axial location. At this firstlocation, the sealing contact 16 is provided by the first seal member 22a which is disposed adjacent to and seals against the valve sleeve 44 ofthe downhole tool 12.

However, as the dart 10 progresses in the direction of arrow 90, sealmember 22 a will become aligned with ports 92 defined in the valvesleeve (which are used, eventually, to become aligned with ports 42).Accordingly, seal member 22 a will loose its sealing function. However,at this point sealing member 22 b will become aligned with cylindricalsurface 94 on the tool 12, and as such will now establish sealingcontact.

As the dart 10 continues to progress, the particular seal memberproviding a sealing function may vary, and as such permitting at leastone sealing contact to be achieved at all times during passage of thedart 10 through the downhole tool 12.

It should be understood that the embodiments described herein are merelyexemplary and that various modifications may be made thereto withoutdeparting from the scope of the invention.

For example, it will be recognised that a wellbore system may comprise aplurality of darts 10 and downhole tools 12 of the same or differentconfiguration and a dart 10 may be provided behind a column of cement 14and used to drive cement 14 through the downhole tool 12 or may belocated ahead of a column of cement and used, for example, to deploy aninhibitor in the downhole tool 12 prior to the cementing operation.

Referring now to FIGS. 6 to 9, there is shown a wellbore system 100including a drilled borehole 102 which extends from surface 104 andintercepts a subterranean reservoir or formation 106. In the illustratedembodiment, the borehole 102 may comprise a deviated, high angle orhorizontal section 108.

The formation 106 may contain hydrocarbons to be produced to surface 104via the system 100. Alternatively, or additionally, the subterraneanformation 106 may define a target for receiving a treatment medium orfluid injected from surface 104 via the system 100, for example forincreasing formation pressure to improve production of hydrocarbons fromthe formation 106 or a neighbouring formation, for sequestrationpurposes, or the like.

A tubular string 110 extends through the borehole 102, the string 1110comprising a plurality of fracturing tools 112 distributed along itslength at a desired interval spacing. One of more of the tools 112 may,for example, comprise a tool such as the tool 12 described above.

FIG. 6 shows the wellbore system 100 after location of a tubular string110 at a required depth.

A number of operations may be required during the life cycle of thewellbore system 100 which require the ability to direct a fluid intoand/or from the formation 106. For example, a cementing operation may becarried out in order to assist in securing and supporting at least partof the string 110 in the borehole 102, to prevent uncontrolled migrationof fluid in annulus 114 between the string 110 and the borehole 102and/or in the isolation of particular formation zones prior to perform afracturing or stimulation operation.

Referring to FIG. 7, the cementing operation may involve directing avolume of cement 116 through the string 110 which is then directed intothe annulus 114 and circulated back towards surface to fill the annulus114 or an annulus section.

In order to control the cementing process, a first cement apparatus maydisposed ahead of the cement 116 and engage a landing collar (not shown)while a second cement apparatus is disposed behind the column of cement116. The first cement apparatus may comprise a dart 118, similar to oridentical to the dart 10 described above. The second cement apparatusmay also or alternatively comprise a dart 120, similar to or identicalto the dart 10 described above. Increased pressure may then be used torupture or open a fluid passage so that the cement 116 may be driveninto the annulus 114. In use, the second dart 120 may also act to cleanany cement 116 as it is driven through the string 110 which mayotherwise form an obstruction. The cemented borehole is shown in FIG. 8.

Alternatively or additionally, the formation 106 may require stimulationor treatment to provide improved production or injection rates to beachieved or restored. Stimulation techniques include hydraulicfracturing which involves injecting a fracturing fluid into theformation at high pressure and/or flow rates to create mechanicalfractures within the geology. These fractures may increase the effectivenear-wellbore permeability and fluid connectivity between the formationand wellbore. The fracturing fluid may carry proppant material, whichfunctions to prop open the fractures when the hydraulic fracturingpressure has been removed. Matrix stimulation provides a similar effectas hydraulic fracturing. This typically involves injecting a chemicalsuch as an acid, for example hydrochloric acid, into the formation tochemically create fractures or wormholes in the geology. Such matrixstimulation may have application in particular geology types, such as incarbonate reservoirs.

As shown in FIG. 9, each of the tools 112 includes a plurality ofcircumferentially arranged ports 122, which are initially closed.Further, each tool 112 includes or is associated with a downholeactuator (not shown) which is operable to actuate the tool 112 to openthe associated ports 122 to allow injection of a treating fluid, such asa fracturing fluid or acid, from the string 110 into the surroundingformation 106 to create fractures 124. Each tool 112 is operated byactuation objects, such as balls, which are delivered through the string110 from surface 104.

The tools 112 are capable of being actuated in a desired sequence, thusallowing the formation 106 to be treated along the length of theborehole 102 in stages. Such ability to actuate the tools 112sequentially may be achieved via the associated downhole actuator. Inthe illustrated embodiment, the tools 112 are arranged to be actuated inan uphole sequence or direction. This is shown in FIG. 9 in which thelowermost illustrated tool 112 has previously been actuated, with anadjacent tool 112 on the uphole side shown in an actuated state withfracturing fluid from the opened ports 122 being directed into theformation 106 in the direction of arrows 126. Once appropriatefracturing has been achieved via tool 112, the next uphole tool 112 maythen be actuated.

1. A downhole cementing apparatus deployable through a downhole toolwith a volume of cement, comprising: a body; and a sealing arrangementmounted on the body and configured to define a varying point of sealingcontact axially along the sealing arrangement with an inner surface of adownhole tool as the cementing apparatus is deployed through said tool.2. The apparatus of claim 1, wherein providing a varying point ofsealing contact permits a seal to be provided at all times duringpassage of the apparatus through the downhole tool.
 3. The apparatus ofclaim 1, wherein the sealing arrangement comprises at least one sealmember for sealingly engaging the inner surface of the downhole tool. 4.The apparatus of claim 3, wherein at least one seal member is operableto swab or wipe the inside of the downhole tool during deploymentthrough said tool.
 5. The apparatus of claim 1, wherein the sealingarrangement comprises a plurality of seal members arranged along thebody.
 6. The apparatus of claim 4, comprising at least one spacer toprovide an axial spacing between at least two seal members.
 7. Theapparatus of claim 5, wherein the seal members are spaced so that atleast one seal member provides sealing contact with the inner surface ofthe downhole tool during deployment through said tool.
 8. The apparatusof claim 5, wherein the radial extent of the seal members is configuredsuch that at a first axial location in the downhole tool a first sealmember cooperates with the downhole tool to provide a sealing contact,and at a second axial location within the downhole tool the first sealmember does not provide sealing contact and a second seal membercooperates with the downhole tool to provide a sealing contact.
 9. Theapparatus of claim 3, wherein at least one seal member defines a cupshape.
 10. The apparatus of claim 3, wherein at least one seal memberdefines a disc shape.
 11. The apparatus of claim 3, wherein at least oneseal member is disposed on a mandrel.
 12. The apparatus of claim 11,wherein the mandrel comprises at least one module.
 13. The apparatus ofclaim 11, wherein the mandrel comprises a plurality of modules.
 14. Theapparatus of claim 11, wherein at least one module supports at least oneseal member.
 15. The apparatus of claim 11, wherein an identifier isprovided to facilitate identification of at least one module or sealmember.
 16. The apparatus of claim 11, wherein the mandrel comprises atleast one spacer module for providing an axial spacing between at leasttwo seal members.
 17. The apparatus of claim 12, wherein a connectionarrangement is provided for coupling at least two modules of the mandreltogether.
 18. The apparatus of claim 1, wherein the downhole toolcomprises a tool for use in treating a subterranean formation.
 19. Theapparatus of claim 1, wherein the downhole tool comprises a tool for usein fracturing a subterranean formation.
 20. The apparatus of claim 1,wherein the apparatus is deployable through an axial flow passage orthroughbore of the downhole tool.
 21. A downhole method comprising:deploying an apparatus through a downhole tool, wherein the apparatuscomprises a sealing arrangement; establishing a point of sealing contactbetween the sealing arrangement and an inner surface of the downholetool; and varying the point of sealing contact axially along the sealingarrangement during deployment through the downhole tool.
 22. The methodof claim 21, comprising providing the varying point of sealing contactbetween a plurality of axially spaced seal members within the sealingarrangement.
 23. The method of claim 22, wherein at a first axiallocation within the downhole tool, a first seal member cooperates withthe downhole tool to provide a first point of sealing contact.
 24. Themethod of claim 23, wherein at a second axial location within thedownhole tool the first point of sealing contact is removed, and asecond seal member cooperates with the downhole tool to provide a secondpoint of sealing contact.
 25. The method of claim 21, comprising pumpingthe apparatus through the downhole tool.
 26. The method of claim 21,comprising passing a volume of cement through the downhole tool on oneaxial side of the apparatus.
 27. The method of claim 21, comprising:deploying first and second apparatuses through the downhole tool,wherein each apparatus includes a respective sealing arrangement;deploying a volume of cement intermediate the first and secondapparatuses; establishing a point of sealing contact between therespective sealing arrangements and an inner surface of the downholetool; and varying the respective points of sealing contact axially alongthe respective sealing arrangements during deployment through thedownhole tool.
 28. The method of claim 21, comprising or forming part ofa downhole cementing operation.
 29. The method of claim 21, comprisingtreating a subterranean formation via the downhole tool.
 30. The methodof claim 21, wherein the downhole tool comprises a tool for use infracturing a subterranean formation.
 31. A downhole system, comprising:a downhole tool; and an apparatus for deployment through the downholetool, wherein the apparatus comprises a sealing arrangement configuredto define a varying point of sealing contact axially along the sealingarrangement with an inner surface of the downhole tool during deploymentthrough said tool.
 32. The downhole system of claim 31, wherein theapparatus comprising a plurality of axially spaced seal members, whereinthe axial spacing of the seal members is configured such that at a firstaxial location in the downhole tool one of the seal members cooperateswith the downhole tool to provide a sealing contact and at a secondaxial location within the downhole tool said seal member permits passageof fluid and at least one other of the seal members cooperates with thedownhole tool to provide a sealing contact.
 33. The downhole system ofclaim 31, wherein the downhole tool comprises a tool for use in treatinga subterranean formation.
 34. The downhole system of claim 31, whereinthe downhole tool comprises a tool for use in hydraulic fracturing. 35.The downhole system of claim 31, wherein the downhole tool comprises atool housing defining a central bore and including a fluid port.
 36. Thedownhole system of claim 31, wherein the downhole tool comprises a valvesleeve.
 37. The downhole system of claim 31, wherein the downhole toolcomprises a catching apparatus.
 38. The downhole system of claim 31,wherein the downhole tool comprises an indexing mechanism.
 39. A methodfor inhibiting adherence of cement to a downhole tool of a string,comprising coating a surface of the tool with sugar grease.
 40. Themethod of claim 39, comprising directing a volume of sugar greasethrough the string.
 41. The method of claim 39, wherein the downholetool comprises a tool for use in treating a subterranean formation. 42.The method of claim 39, wherein the downhole tool comprises a tool foruse in hydraulic fracturing.
 43. The method of claim 39, wherein thedownhole tool comprises a tool housing defining a central bore andincluding a fluid port.
 44. The method of claim 39, wherein the downholetool comprises a valve sleeve.
 45. The method of claim 39, wherein thedownhole tool comprises a catching apparatus.
 46. The method of claim39, wherein the downhole tool comprises an indexing mechanism.
 47. Themethod of claim 39, comprising directing a volume of cement through thedownhole tool.
 48. The method of claim 39, comprising using a downholeapparatus comprising a body and a sealing arrangement mounted on thebody to direct sugar grease through the downhole tool.
 49. A downholecementing method, comprising: directing a volume of cement through astring comprising a fracturing tool; and directing the cement into anannulus surrounding at least a portion of the string.
 50. The method ofclaim 49, comprising performing a fracturing operation after the cementhas been directed into the annulus.
 51. The method of claim 49,comprising deploying an apparatus through the string with the volume ofcement, wherein the apparatus comprises: a body; and a sealingarrangement mounted on the body and configured to define a varying pointof sealing contact axially along the sealing arrangement with an innersurface of a downhole tool as the cementing apparatus is deployedthrough said tool.
 52. The method of claim 49, comprising disposing afirst apparatus on a downhole side of the volume of cement.
 53. Themethod of claim 52, comprising disposing a second apparatus on an upholeside of the cement.
 54. The method of claim 49, comprising coatingsurfaces of the fracturing tool with an inhibitor configured to inhibitadherence of cement to the surface.